Warm Rain and Hot Wind On the Way

May 12, 2008

SnapshotBack to work today after a so-so weekend weatherwise.  Forecast was pretty good, but a bit chilly again for early May.  Apparently we’ll make up for that later this week.  Several items of interest:

1.  Rain
Tropical moisture is streaming across the East Pacifc towards the West Coast tonight.  Models bring some of that inland tomorrow for a cloudy and sometimes rainy day in Northwest Oregon and Southwest Washington.  Not much to debate here.  It is strange to have rain forecast at the same time upper level heights near 580dm at 500mb.  The 00z GFS pushes rain north of us soon after daybreak Wednesday, with plenty of afternoon sunshine.  That plus a very warm atmosphere should push us into the low-mid 70s that day.

2. Hot Temps
No argument on the big heat up for Thursday-Saturday either.  Models have been very consistent for the last 24 hours.  Offshore flow begins on Thursday…in fact GFS has the thermal trough out along the beaches already in the morning.  Easterly flow + 850mb temps around +18degC equals a high right around 90 here in Portland.  So we’ll go from low-mid 70’s Wednesday to 90 Thursday…quite  a change.  Then I notice the last few runs of GFS and ECMWF (as of 12z) show no significant onshore push of marine air until Saturday night.  So…another day of even strong offshore flow Friday + 850mb temps of 20-22 degC should give us a high awfully close to 95.  On my chart, I see only 4 days in 9 years during the month of May have seen 850 mb temps above +20.  This will be a very rare hot spell indeed, especially if we do see 2-3 days at/above 90 degrees.  Just think, overnight temps in the city will be quite close to today’s high!  I almost planted some more summer veggies today, but figured it would be better to wait for much warmer soil Sunday or Monday AFTER the extreme and stressful heat has passed. 

3.  Dry May
We’ve seen very little rain this month and apparently very little is going to fall through the 20th based on current maps.  For those of you with freshly planted vegetation, you need to water the next few days…really soak those new shrubs because they’ll be fighting a dry, hot east wind Thursday and Friday.  These plants have gotten used to 55-65 degree days and some drips.

Mark Nelsen